Topic review.

Congruence preserves both shape and size; corresponding vertex order records which parts match.

Use SSS, SAS, ASA/AAS or RHS with the correct included-angle or right-angle conditions.

Similarity preserves angles and uses one common factor for corresponding lengths.

A diagonal can turn a quadrilateral claim into a congruent-triangle argument.

Rigid transformations preserve congruence; equal-factor enlargements preserve similarity.

Algorithms need complete decisions. Digital measurements test a claim but are not a universal proof.